\begin{tabular}{l*{4}{l}}
\toprule
                    &\multicolumn{4}{c}{}                               \\
                    &$ z_{i}^{(1)}$&$ z_{i}^{(2)}$&$\text{Upstreamness}_{ni}$&$\text{InputSimilarity}_{ni}$\\
\midrule
$ z_{i}^{(1)}$     &        1.00&            &            &            \\
$ z_{i}^{(2)}$     &        0.85&        1.00&            &            \\
$\text{Upstreamness}_{ni}$&       -0.27&       -0.25&        1.00&            \\
$\text{InputSimilarity}_{ni}$&        0.13&        0.12&       -0.23&        1.00\\
\bottomrule
\end{tabular}
